This is a battery connector cap for XT60 connectors, with an integral indicator showing the state of the battery (full/empty, plus storage). This also works for EC3 connectors (with a little bit of tweaking & squeezing when installing). Handy when flying RC planes or driving RC vehicles out in the field with multiple batteries. No longer will you wonder which ones are full and which are used!
There are 4 parts to the design, I elected to print the inner and outer sleeves as yellow, to match the XT60 connectors and be easy to see when you drop them in the field. The indicator will need to be printed in at least red/green, read the notes below regarding print settings for addition of a white backing layer for 'pop'. The storage cap I printed in black for maximum contrast.
This goes without saying, but there are some precise tolerances in these prints, so ensure your printer is properly calibrated for best results. Hopefully, you won't need to scale up/down, but it might be required depending on your particular setup and your preferred 'grip' on the connector.
Printing directions (these orientations produce the best results): Print the Outer with the tiny indicator notches closest to the plate, and make sure you have enough squish on your first layer to get good adhesion as there is a chamfer on the edges to soften them. I've had a few rat's nests on multi-unit prints because of this. The Inner should be printed with the notches up, for least distortion. The Indicator can be printed flat, and the Storage cap can be printed face-down, as you'd expect.
Assembly instructions: I found the easiest way to assemble everything is to lay the Indicator into the Outer sleeve, and get it positioned with a pen, etc. Then, use an XT60 connector to press it down into place, and lightly click into the notches. Once that's in place, take the Inner sleeve, notches facing down, and carefully press it into the Outer sleeve on a hard surface (so you don't pop the Indicator out when holding it from below). Press down until the Inner is fully seated, and then flip the whole assembly over and press down (on the edges only!) firmly to ensure everything is tight. You'll probably get another little 'click', which tells you it's all happily mated. The bottom of the Inner and Outer should be flush if correctly seated.
Now, use a pen clip or paperclip to gently rotate the indicator a few times. It's designed to be a bit tight at install to keep the tolerances tight during use. Rotate the indicator in both directions to round the sharp edges, until you can comfortably rotate with your fingernail like you would in the field. Install on your XT60!
The Storage cap snaps right over the top of the entire assembly, and can be most easily removed by gently pulling the pointed end of the face and rotating it away from the connector at an angle. The whole cap (including Storage cap) can be completely removed by simply squeezing the sides when pulling, to keep it connected to the indicator cap.